This invention relates to compositions of matter comprising phosphorodithioate derived succinic anhydride derivatives and their corresponding metal salts and to lubricant and liquid fuel compositions containing small additive amounts thereof.
Lubricants, such as lubricating oils and greases, are subject to oxidative deterioration at elevated temperatures or upon prolonged exposure to the elements. Such deterioration is evidenced, in many instances, by an increase in acidity and in viscosity, and when the deterioration is severe enough, it can cause metal parts to corrode. Additionally, severe oxidation leads to a loss of lubrication properties, and in especially severe cases this may cause complete breakdown of the device being lubricated. Many additives have been tried, however, many of them are only marginally effective except at high concentrations. Improved antioxidants are clearly needed.
Antioxidants or oxidation inhibitors are used to minimize the effects of oil deterioration that occur when hot oil is contacted with air. The degree and rate of oxidation will depend on temperature, air and oil flow rates and, of particular importance, on the presence of metals that may catalytically promote oxidation. Antioxidants generally function by prevention of chain peroxide reaction and/or metal catalyst deactivation. They prevent the formation of acid sludges, darkening of the oil and increases in viscosity due to the formation of polymeric materials.
Water (moisture) is another critical problem. In spite of even extraordinary precautionary efforts water is found as a film or in minute droplets in vessels containing various hydrocarbon distillates. This brings about ideal conditions for corrosion and damage of metal surfaces of the vessels and the materials contained therein. Also in the lubrication of internal combustion engines, for example, quantities of water are often present as a separate phase within the lubricating system. Another serious problem in respect to metallic surfaces in contact with adjacent metallic surfaces is the surface wear caused by the contact of such surfaces. One material capable of simultaneously effectively coping with such problems as these is highly desireous.
It has now been found that the use of phosphorodithioate derived succinic anhydride derivatives and their corresponding metal salts provide exceptional antioxidant and antiwear activity with significant rust inhibiting, and potential corrosion inhibiting properties. These remarkable benefits are to be expected for a variety of synthetic and mineral oil based lubricants and liquid hydrocarbon fuels.
To the best of our knowledge, these compositions have not been previously used as multifunctional additives in lubricating oils, greases, or fuel applications. The additive products themselves and lubricant compositions thereof are both believed to be novel.
The use of phophorodithioate compositions, especially the corresponding salts of phosphorodithioate, such as Zinc dialkylphosphorodithioates (commonly known as zinc dithiophosphates) have found widespread commerical use for several decades in engine oils as multifunctional antiwear, peroxide decomposing, and bearing corrosion inhibiting additives.
The use of succinic anhydride derivatives has been extensively reported as having beneficial antirust properties as well as detergency/dispersancy characteristics. It is an object of this invention to provide lubricant and fuel compositions of improved multifunctional capability having, e.g. antioxidant, antiwear and antirust/corrosion characteristics. It is a further object to provide novel additive products derived form phosphorodithioate substituted carboxylic acid anhydride derivatives and their corresponding metal salts.